The invention relates to a continuous method for preparing high cis-1,4 polybutadiene. More particularly, the invention relates to a continuous method of preparing high cis-1,4 polybutadiene by continuously polymerizing 1,3-butadiene in solution under adiabatic conditions by a procedure which involves continuously feeding to a single agitated polymerization reactor a 1,3-butadiene monomer stream, a preformed .pi. allyl catalyst stream, and a cocatalyst stream while withdrawing high cis-1,4 polybutadiene at the same rate as said monomer, preformed catalyst and cocatalyst streams are fed to the reactor.
Various methods for preparing high cis-1,4 polybutadiene using catalyst systems comprising organonickel or organocobalt compounds, organo-aluminum compounds such as trialkyl aluminum compounds and fluorine-containing compounds such as boron trifluoride complexes, hydrogen fluoride and hydrogen fluoride complexes have been known in the prior art as illustrated, for example, by U.S. Pat. Nos. 3,170,907; 3,464,865; 3,371,462; 3,483,177; 3,487,063; 3,528,957; 3,769,270; and 3,985,941. However, the processes described in the above patents suffer from the significant disadvantage that they are batch-type polymerization processes. From a commercial standpoint, batch-type polymerization processes are not as desirable as continuous polymerization processes as the latter permits much greater production rates.
More recently, continuous polymerization processes have been proposed in the prior art. Thus, British Pat. No. 1,499,638 relates to a method of preparing high cis-1,4 polybutadiene which comprises continuously polymerizing butadiene in admixture with a reaction medium comprising an inert aliphatic or cycloaliphatic hydrocarbon employing as a catalyst a CS.sub.2 -free mixture comprising (A) at least one trialkyl aluminum wherein the alkyl group contains from 2 to 8 carbon atoms, (B) at least one nickel salt of a carboxylic acid, and (C) at leat one boron trifluoride complex with an ether in which each of the individual catalyst components are continuously separately injected into the polymerization vessel containing the mixture of the butadiene and the inert aliphatic or cycloaliphatic reaction medium.
European Patent Application No. 83630072.3 relates to a process for controlling the molecular weight of high cis-1,4 polybutadiene which comprises polymerizing 1,3-butadiene under solution polymerization conditions employing as a catalyst (1) at least one organoaluminum compound; (2) at least one organonickel compound selected from the group consisting of nickel salts of carboxylic acids, organic complex compounds of nickel and nickel tetracarbonyl; and (3) hydrogen fluoride or a hydrogen fluoride complex prepared by complexing hydrogen fluoride with a complexing compound of the group consisting of ketones, aldehydes, nitriles, esters, ethers, alcohols, phenols, mineral acids containing oxygen and water or mixtures thereof; wherein the polymerization is conducted at a temperature of from about 68.degree. C. to about 107.degree. C.; wherein the polymerization is conducted in the presence of small amounts of an olefin selected from the group consisting of ethylene, propylene, 1-butene, cis and trans 2-butene, 1,5-hexadiene, 1,4-hexadiene, 1,4-pentadiene, and 1,6-heptadiene and wherein the polymerization is a continuous process.
The processes described in the above British patent and the European patent application appear to be entirely distinguishable from the process of the present invention. Thus, the British patent and the European patent application both utilize a different nickel catalyst component than that employed in the process of the invention. In addition, both of these references appear to require that the catalyst addition be conducted by the in-situ addition method in which the individual catalyst components, i.e. the nickel compound, the organoaluminum compound and the fluorine compound (e.g. hydrogen fluoride, hydrogen fluoride complex, and boron trifluoride etherate) are separately injected into the polymerization zone. Moreover, the European patent application additionally requires the polymerization to be conducted in the presence of a small amount of an olefin.
The processes described in the British patent and the European patent application have the significant advantage of being continuous processes. However, the aforementioned processes also suffer from several significant disadvantages which materially limit their usefulness as commercial production processes. Thus, as disclosed in the Examples of the British patent and European patent application, the processes described therein utilize two (2) polymerization reactors connected in a chain or series. Moreover, as further disclosed in the examples therein, the rate of conversion of monomer to polymer is lower than desirable and the residence times longer than desirable for many commercial operations. Thus, the British patent process which utilizes two polymerization reactors achieves an average rate of conversion of about 75% at an average residence time of about 4.3 hours while the European patent application process, which also utilizes two polymerization reactors, achieves a rate of conversion of about 85% and residence times of from 2.5 to 3.0 hours (Example 1) and 1.5 to 2.0 hours (Example 2).
As will be evident from the foregoing, the discovery of a continuous process for preparing high cis-1,4 polybutadiene using a single reactor and which results in higher conversion rates at shorter residence times would constitute a significant advance over the processes of the British patent and the European patent application.